The mutual solubility for the ternary p-nitroaniline + o-nitroaniline + ethanol system was measured at (273.15 to 323.15) K. Three isothermal phase diagrams of the system were constructed on the basis of the measured solubilities. The phase diagrams of the ternary system were similar at all temperatures investigated. Two solid phases were formed and confirmed by the Schreinemaker's wet residue method; one was p-nitroaniline, and the other was o-nitroaniline. The crystallization regions of p-nitroaniline and o-nitroaniline increase as the temperature decreases. At the same temperature, the crystallization region of p-nitroaniline is larger than that of o-nitroaniline.